Expressions of tumor immunity at the tumor site are an essential component of the tumor-host immunological relationship. The present proposal deals with humoral tumor immunity in situ. It is now clear that immunoglobulin (Ig) is present in non-lymphoid human and animal tumors. In view of the generality of this in vivo phenomenon and in view of findings implying biological functions mediated by these Ig molecules, it is essential to study the nature of the tumor-bound Ig molecules and to elucidate their role in tumor growth and in the host-tumor relationship. We propose to characterize immunochemically tumor-bound Igs and in particular whether such molecules when eluted from the cells (eluate Ig) are in complex with tumor antigen. It is also proposed to study the affinity of eluate-Ig towards tumor cells. We will study functions of tumor bound Ig in relation to various in vitro expressions of anti-tumor cellular immunity, in particular whether it can block or alternatively potentiate cellular immunity. The effects of eluate Ig on tumor growth in vivo and on the profile of host cells in in vivo propagating tumors will be studied as well. We will also investigate the in vivo localization properties of Ig eluted from tumors. We intend to characterize the cells in tumors (whether host or tumor cells) to which Ig is bound. The question whether tumor-bound Igs are anti-tumor antibodies will be investigated using tumor systems in which antigenic specificities are well characterized, such as antigens of a Polyoma virus induced tumor or of MuLV. We intend to investigate in vivo aspects of degradation of anti-tumor antibodies by proteases of tumor origin. Finally, we will study the effects of unrelated immune complexes and of Fc-receptor bearing cells on tumor growth.